Method for polymerizing α-olefins in a gaseous phase

ABSTRACT

alpha-Olefins are polymerized in the gas phase at from 30 to 150  C. and a pressure of from 5 to 80 bar using a catalyst or a catalyst mixture containing as antistatic agent from 0.1 to 5% by weight of ZnO and/or anhydrous MgO, based on the total amount of the catalyst mixture, except for a process in which the catalyst mixture comprises a chromium catalyst and MgO-supported Ziegler catalyst which is modified with an alkene and with alkylaluminum hydride and also comprises free MgO and the total amount of the MgO is not less than 2% by weight of the catalyst mixture

The present invention relates to a process for the polymerization ofα-olefins in the gas phase at from 30 to 125° C. and a pressure of from5 to 80 bar.

The present invention further relates to the use of MgO and/or ZnO as.antistatic agent in this polymerization process.

The polymerization of α-olefins in the gas phase frequently results information of deposits on the walls of the reactor and to the formationof lumps. This formation of deposits and lumps is at least partiallyattributable to electrostatic charging. The formation of deposits leadsto blockages in the product discharge system and thereby hinders thecontinuous operation of such gas-phase plants.

Electrostatic charging is influenced in a complex manner by numeroussystem parameters in the gas-phase polymerization process, for exampleby the particle size distribution of the polymer and of the catalyst,the chemical composition of the catalyst, the reaction temperature, thereaction pressure and the composition of the circulating gas.

U.S. Pat. No. 5,391,657 describes a method by which deposit formation ingas-phase polymerizations of α-olefins can be prevented by addinginorganic additives (MgO, ZnO, Al₂O₃, CuO and mixtures of these) whichgenerate positive charges or inorganic additives (V₂O₅, SiO₂, TiO₂,Fe₂O₃ and mixtures of these) which generate negative charges as afunction of the particular electrostatic charging situation in thereactor. However, this method requires the continual measurement of theelectrostatic charge and also a metering-in system which is regulated ina complex manner as a function of this measurement, and the method istherefore associated with a considerable outlay in terms of apparatus.

Catalysts or catalyst systems which comprise MgO as support material oras a modifying additive are also already known from the literature.Thus, U.S. Pat. No. 5,408,015 describes a catalyst system comprising achromium oxide catalyst, a Ziegler catalyst supported on MgO and alsofrom about 1 to 15% by weight of MgO as additives. The ratio of chromiumoxide catalyst to MgO-supported Ziegler catalyst is from 6:1 to 100:1,so that the overall mixture contains at least 2% by weight of MgO. Theaddition of MgO makes it possible to prepare ethylene polymers orcopolymers (HDPE) having a broad molecular weight distribution andproperties which are particularly advantageous for blow molding,applications.

U.S. Pat. No. 4,946,914 describes a supported catalyst which is producedby combining a chromium-containing catalyst with a modifier, viz. anoxide of an element of group IIa of the Periodic Table of the Elements.MgO is mentioned as an example of a modifier. The modifier is added inorder to obtain polymers having a higher high load melt index (HLMI)than those obtained using a catalyst system without this modifier. Forthis purpose, it is said to be important that the modifier contains atleast 0.5% by weight, for best results about 2% by weight, of water.

The previously known methods for preventing electrostatic charging inthe gas-phase polymerization of α-olefins still leave something to bedesired in respect of their effectiveness or their technical complexity.

It is an object of the present invention to find a process forpolymerizing α-olefins in the gas phase in which the formation ofdeposits on the reactor walls and at the bottom of the reactor can beprevented in a simple and efficient manner.

We have found that this object is achieved by a process for thepolymerization of α-olefins in the gas phase at from 30 to 150° C. and apressure of from 5 to 80 bar, wherein use is made of a catalyst or acatalyst mixture containing as antistatic agent from 0.1 to 5% by weightof ZnO and/or anhydrous MgO, based on the total amount of the catalystmixture except for a process in which the catalyst mixture comprises achromium catalyst and an Mgo-supported Ziegler catalyst which ismodified with an alkene and with alkylaluminum hydride an also comprisestree MgO and the total amount of the MgO is not less than 2% by weightof the catalyst mixture.

The process of the present invention enables especially ethylene andpropylene and in particular ethylene to be homopolymerized orcopolymerized. Particularly suitable comonomers are α-olefins havingfrom 3 to 8 carbon atoms. A process in which mixtures of ethylene withC₃-C₈-α-olefins are copolymerized is particularly advantageous.C₃-C₈-α-olefins which are useful in such a copolymerization are, inparticular, propene, butene, pentene, 4-methylpentene, hexene, hepteneand octene, and also mixtures of these.

The polymerization process is carried out at from 30 to 125° C.,preferably from 80 to 120° C. The pressure is from 5 to 80 bar,preferably from 20 to 60 bar.

The polymerization can be carried out by various gas-phase methods, ie.for example in gas-phase fluidized beds or in stirred gas phases.

The antistatic agent used is ZnO and/or anhydrous MgO. In this context,anhydrous means that the water content of the MgO should be less than0.5% by weight, preferably less than 0.3% by weight, based on the totalmass of the MgO. The ZnO too is preferably used in anhydrous form. Thedewatering of the oxides is most simply carried out by heating underreduced pressure, for example to from 150 to 450° C. under reducedpressure. The drying time depends on the temperature selected. Goodresults are achieved, for example, at 250° C. under reduced pressure fora period of 8 hours.

Among the oxides having an antistatic effect, ZnO is worthy ofparticular emphasis.

The antistatic agent or the mixture of the two antistatic agents isadded to the catalyst or the catalyst mixture in an amount of from 0.1to 5% by weight, based on the total amount of catalyst or catalystmixture. The antistatic agent is preferably present in the catalyst orthe catalyst mixture in an amount of more than 0.2% by weight and lessthan 2% by weight.

The oxides which have an antistatic effect can be used in a wide varietyof particle sizes. The oxides are particularly effective if they arevery fine. Thus, mean particle diameters of from 10 to 200 μm, inparticular from 20 to 100 μm, have been found to be particularly useful.Also advantageous are particle diameters which are similar to the sizeof the catalyst particles.

In the process of the present invention it is possible to use variouscatalysts as are customary for the polymerization of α-olefins. Thus,suitable catalysts are, for example, the supported chromium catalystsalso known as Phillips catalysts.

The application of soluble chromium compounds to support materials isgenerally known. Suitable support materials are especially inorganiccompounds, in particular porous oxides such as SiO₂, Al₂O₃, MgO, ZrO₂,TiO₂, B₂O₃, CaO, ZnO or mixtures of these. The support materialspreferably have a particle diameter of from 1 to 300 μm, in particularfrom 30 to 70 μm. Examples of particularly preferred supports are silicagels and aluminosilicate gels, preferably those of the formula SiO₂.aAl₂O₃, where a is a number from 0 to 2, preferably from 0 to 0.5; theseare thus aluminosilicates or silicon dioxide. Such products arecommercially available, eg. silica gel 332 from Grace.

The doping of the catalyst support with the chromium-containing activecomponent is generally carried out from a solution or, in the case ofvolatile compounds, from the gas phase. Suitable chromium compounds arechromium(VI) oxide, chromium salts such as chromium(III) nitrate andchromium(III) acetate, complexes such as chromium(III) acetylacetonateor chromium hexacarbonyl, or else organometallic compounds of chromium,eg. bis(cyclopentadienyl)chromium(II), organic esters of chromium(VI)acid or bis(arene)chromium(O).

The active component is generally applied to the support by bringing thesupport material in a solvent into contact with a chromium compound,removing the solvent and calcining the catalyst at from 400 to 1100° C.For this purpose, the support material can be suspended in a solvent orelse in a solution of the chromium compound.

Apart from the chromium-containing active component, further dopants canbe applied to the support system. Examples of such possible dopants arecompounds of boron, of fluorine, of aluminum, of silicon, of phosphorusand of titanium. These dopants are preferably applied together with thechromium compounds to the support, but can also be applied to thesupport in a separate step before or after the chromium.

Examples of suitable solvents for doping the support are water,alcohols, ketones, ethers, esters and hydrocarbons.

The concentration of the doping solution is generally 0.1-200 g ofchromium compound/l of solvent, preferably 1-50 g/l.

The weight ratio of the chromium compounds to the support during dopingis generally from 0.001:1 to 200:1, preferably from 0.005:1 to 100: 1.

A preferred embodiment of the invention provides for the chromiumcatalyst to be produced by adding the desired amount of MgO and/or ZnOto the inactive catalyst precursor and subsequently activating thismixture in a customary manner.

For the activation, the dry catalyst precursor is, for example, calcinedat from 400 to 1100° C., in an oxidizing, oxygen-containing atmospherein a fluidized-bed reactor. Cooling is preferably carried out under aninert gas atmosphere in order to prevent adsorption of oxygen. Thiscalcination can also be carried out in the presence of fluorinecompounds such as ammonium hexafluorosilicate, as a result of which thecatalyst surface is modified with fluorine atoms. The calcination ispreferably carried out at from 500 to 800° C.

Furthermore, Ziegler catalysts or Ziegler-Natta catalysts can also beused in the process of the present invention. Customary catalysts ofthis type are described, for example, in Ullmann's Encyclopedia ofIndustrial Chemistry, Vol. A 21, 4th Edition 1992, p. 502 ff. Particularmention should here be made of those catalysts as are described, forexample, in U.S. Pat. No. 4,857,613 and in DE-A-19 529 240.

In a further preferred embodiment of the process of the presentinvention, a metallocene catalyst is used as catalyst or as constituentof the catalyst mixture.

Suitable metallocene catalysts are, for example, those in which theparticulate organic or inorganic support material used is a polyolefinsuch as polyethylene, polypropylene, poly-1-butene orpolymethyl-1-pentene or a copolymer comprising the monomers on whichthese polymers are based, or else a polyester, polyamide, polyvinylchloride, polyacrylate, polymethacrylate or polystyrene. However,preference is given to inorganic support materials such as porousoxides, eg. SiO₂, Al₂O₃, MgO, ZrO₂, TiO₂, B₂O₃, CaO, ZnO. Metal halidessuch as MgCl₂ are also suitable as supports. The support materialspreferably have a particle diameter of from 1 to 300 μm, in particularfrom 30 to 70 μm. Particularly preferred supports are, for example,silica gels, preferably those of the formula SiO₂.a Al₂O₃, where a is anumber from 0 to 2, preferably from 0 to 0.5; these are thusaluminosilicates or silicon dioxide. Such products are commerciallyavailable, eg. silica gel 332 from Grace.

Particularly suitable metallocene catalysts are those comprisingmetallocene complexes of the formula I

were the substituents have the following meanings:

M is titanium, zirconium, hafnium, vanadium, niobium or tantalum

X is fluorine, chlorine, bromine, iodine, hydrogen, C₁-C₁₀-alkyl,C₆-C₁₅-aryl, alkylaryl having from 1 to 10 carbon atoms in the alkylradical and from 6 to 20 carbon atoms in the aryl radical, —OR⁷ or—NR⁷R⁸,

where

R⁷ and R⁸ are C₁-C₁₀-alkyl, C₆-C₁₅-aryl, alkylaryl, arylalkyl,fluoroalkyl or fluoroaryl each having from 1 to 10 carbon atoms in thealkyl radical and from 6 to 20 carbon atoms in the aryl radical,

R² to R⁶ are hydrogen, C₁-C₁₀-alkyl, 5- to 7-membered cycloalkyl whichmay in turn bear a C₁-C₁₀-alkyl as substituent, C₆-C₁₅-aryl orarylalkyl, where two adjacent radicals may also together form asaturated or unsaturated cyclic group having from 4 to 15 carbon atoms,or Si(R⁹)₃ where

R⁹ is C₁-C₁₀-alkyl, C₃-C₁₀-cycloalkyl or C₆-C₁₅-aryl,

where the radicals

R¹⁰ to R¹⁴ are hydrogen, C₁-C₁₀-alkyl, 5- to 7-membered cycloalkyl whichmay in turn bear a C₁-C₁₀-alkyl as substituent, C₆-C₁₅-aryl orarylalkyl, where two adjacent radicals may also together form asaturated or unsaturated cyclic group having from 4 to 15 carbon atoms,or Si(R¹⁵)₃ where

R¹⁵ is C₁-C₁₀-alkyl, C₆-C₁₅-aryl or C₃-C₁₀-cycloalkyl,

or the radicals R⁵ and Z together form a —R¹⁶—A— group, where

═BR¹⁷, ═AlR¹⁷, —Ge—, —Sn—, —O—, —S—, ═SO, ═SO₂, ═NR¹⁷, ═CO, ═PR¹⁷ or═P(O)R¹⁷,

where

R¹⁷, R¹⁸ and R¹⁹ are identical or different and are each a hydrogenatom, a halogen atom, a C₁-C₁₀-alkyl group, a C₁-C₁₀-fluoroalkyl group,a C₆-C₁₀-fluoroaryl group, a C₆-C₁₀-aryl group, a C₁-C₁₀-alkoxy group, aC₂-C₁₀-alkenyl group, a C₇-C₄₀-arylalkyl group, a C₈-C₄₀-arylalkenylgroup or a C₇-C₄₀-alkylaryl group or two adjacent radicals in each casetogether with the atoms connecting them form a ring, and

M² is silicon, germanium or tin,

A is —O—, —S—,

where

R²⁰ is C₁-C₁₀-alkyl, C₆-C₁₅-aryl, C₃-C₁₀-cycloalkyl, alkylaryl orSi(R²¹)₃,

R²¹ is hydrogen, C₁-C₁₀-alkyl, C₆-C₁₅-aryl which in is turn may bearC₁-C₄-alkyl groups as substituents, or C₃-C₁₀-cycloalkyl

or the radicals R⁵ and R¹³ together form an —R¹⁶— group.

Among the metallocene complexes of the formula I, preference is given to

Particular preference is given to those transition metal complexes whichcontain two aromatic ring systems bridged to one another as ligands, ie.particularly the transition metal complexes of the formulae Ib and Ic.

The radicals X can be identical or different but are preferablyidentical.

Among the compounds of the formula Ia, particular preference is given tothose in which

M is titanium, zirconium or hafnium,

X is chlorine, C₁-C₄-alkyl or phenyl and

R² to R⁶ are hydrogen or C₁-C₄-alkyl.

Preferred compounds of the formula Ib are those in which

M is titanium, zirconium or hafnium,

X is chlorine, C₁-C₄-alkyl or phenyl,

R² to R⁶ are hydrogen, C₁-C₄-alkyl or Si(R⁹)₃,

R¹⁰ to R¹⁴ are hydrogen, C₁-C₄-alkyl or Si(R¹⁵)₃.

Particularly suitable compounds of the formula Ib are those in which thecyclopentadienyl radicals are identical.

Examples of particularly suitable compounds are:

bis(cyclopentadienyl)zirconium dichloride,

bis(pentamethylcyclopentadienyl)zirconium dichloride,

bis(methylcyclopentadienyl)zirconium dichloride,

bis(ethylcyclopentadienyl)zirconium dichloride,

bis(n-butylcyclopentadienyl)zirconium dichloride and

bis(trimethylsilylcyclopentadienyl)zirconium dichloride

and also the corresponding dimethylzirconium compounds.

Particularly useful compounds of the formula Ic are those in which

R² and R¹⁰ are identical and are hydrogen or C₁-C₁₀-alkyl,

R⁶ and R¹⁴ are identical and are hydrogen, methyl, ethyl, isopropyl ortert-butyl,

R³, R⁴, R¹¹ and R¹² have the meanings: R⁴ and R¹² are C₁-C₄-alkyl, R³and R¹¹ are hydrogen or two adjacent radicals R³ and R⁴ or R¹¹ and R¹²may in each case together form a cyclic group having from 4 to 12 carbonatoms,

M is titanium, zirconium or hafnium and

X is chlorine, C₁-C₄-alkyl or phenyl.

Examples of particularly useful complexes are:

dimethylsilanediylbis(cyclopentadienyl)zirconium dichloride,

dimethylsilanediylbis(indenyl)zirconium dichloride,

dimethylsilanediylbis(tetrahydroindenyl)zirconium dichloride,

ethylenebis(cyclopentadienyl)zirconium dichloride,

ethylenebis(indenyl)zirconium dichloride,

ethylenebis(tetrahydroindenyl)zirconium dichloride,

tetramethylethylene-9-fluorenylcyclopentadienylzirconium dichloride,

dimethylsilanediylbis(3-tert-butyl-5-methylcyclopentadienyl)zirconiumdichloride,

dimethylsilanediylbis(3-tert-butyl-5-ethylcyclopentadienyl)zirconiumdichloride,

dimethylsilanediylbis(2-methylindenyl)zirconium dichloride,

dimethylsilanediylbis(2-isopropylindenyl)zirconium dichloride,

dimethylsilanediylbis(2-tert-butylindenyl)zirconium dichloride,

diethylsilanediylbis(2-methylindenyl)zirconium dibromide,

dimethylsilanediylbis(3-methyl-5-methylcyclopentadienyl)zirconiumdichloride,

dimethylsilanediylbis(3-ethyl-5-isopropylcyclopentadienyl)zirconiumdichloride,

dimethylsilanediylbis(2-methylindenyl)zirconium dichloride,

dimethylsilanediylbis(2-methylbenzindenyl)zirconium dichloride

dimethylsilanediylbis(2-ethylbenzindenyl)zirconium dichloride,

dimethylphenylsilanediylbis(2-ethylbenzindenyl)zirconium dichloride,

methylphenylsilanediylbis(2-methylbenzindenyl)zirconium dichloride,

diphenylsilanediylbis(2-methylbenzindenyl)zirconium dichloride,

diphenylsilanediylbis(2-ethylbenzindenyl)zirconium dichloride,

and dimethylsilanediylbis(2-methylindenyl)hafnium dichloride

and also the corresponding dimethylzirconium compounds.

Particularly useful compounds of the formula Id are those in which

M is titanium or zirconium,

X is chlorine, C₁-C₄-alkyl or phenyl,

A is —O—, —S—,

and

R² to R⁴ and R⁶ are hydrogen, C₁-C₁₀-alkyl, C₃-C₁₀-cycloalkyl,C₆-C₁₅-aryl or Si(R⁹)₃ or two adjacent radicals can form a cyclic grouphaving from 4 to 12 carbon atoms.

The synthesis of such complexes can be carried out by methods known perse, with preference being given to reacting the correspondingsubstituted, cyclic hydrocarbon anions with halides of titanium,zirconium, hafnium, vanadium, niobium or tantalum.

Examples of appropriate preparative methods are described in, interalia, Journal of Organometallic Chemistry, 369 (1989), 359-370.

It is also possible to use mixtures of various metallocene complexes.

As a further component, a compound capable of forming metallocenium ionsis also usually present in the catalyst prepared by the process of thepresent invention.

Suitable compounds capable of forming metallocenium ions are strong,uncharged Lewis acids, ionic compounds having Lewis acid cations andionic compounds having Brönsted acids as cations.

As strong, uncharged Lewis acids, preference is given to compounds ofthe formula II

M³X¹X²X³  II

where

M³ is an element of main group III of the Periodic Table, in particularB, Al or Ga, preferably B,

X¹, X² and X³ are hydrogen, C₁-C₁₀-alkyl, C₆-C₁₅-aryl, alkylaryl,arylalkyl, haloalkyl or haloaryl each having from 1 to 10 carbon atomsin the alkyl radical and from 6 to 20 carbon atoms in the aryl radical,or fluorine, chlorine, bromine or iodine, in particular haloaryls,preferably pentafluorophenyl.

Particular preference is given to compounds of the formula II in whichX¹, X² and X³ are identical, preferably tris(pentafluorophenyl)borane.

Suitable ionic compounds having Lewis acid cations are compounds of theformula III

[(Y^(a+))Q₁Q₂ . . . Q_(z)]^(d+)  III

where

Y is an element of main groups I to VI or transition groups I to VIII ofthe Periodic Table,

Q₁ to Q_(z) are groups bearing a single negative charge, eg.

C₁-C₂₈-alkyl, C₆-C₁₅-aryl, alkylaryl, arylalkyl, haloalkyl, haloaryleach having from 6 to 20 carbon atoms in the aryl radical and from 1 to28 carbon atoms in the alkyl radical, C₁-C₁₀-cycloalkyl which may bearC₁-C₁₀-alkyl groups as substituents, halogen, C₁-C₂₈-alkoxy,C₆-C₁₅-aryloxy, silyl or mercaptyl groups,

a is an integer from 1 to 6,

z is an integer from 0 to 5,

d is the difference a−z, but d is greater than or equal to 1.

Particularly useful cations are carbonium cations, oxonium cations andsulfonium cations and also cationic transition metal complexes.Particular mention may be made of the triphenylmethyl cation, the silvercation and the 1,1′-dimethylferrocenyl cation. They preferably havenoncoordinating counterions, in particular boron compounds as are alsomentioned in WO 91/09882, preferably tetrakis(pentafluorophenyl)borate.

Ionic compounds having Brönsted acids as cations and preferably likewisenoncoordinating counterions are mentioned in WO 91/09882; the preferredcation is N,N-dimethylanilinium.

Particularly useful compounds capable of forming metallocenium ions areopen-chain or cyclic aluminoxane compounds of the formula IV or V

where R¹ is C₁-C₄-alkyl, preferably methyl or ethyl, and m is an integerfrom 5 to 30, preferably from 10 to 25.

The preparation of these oligomeric aluminoxane compounds is usuallycarried out by reacting a solution of trialkylaluminum with water and isdescribed, inter alia, in EP-A 284 708 and U.S. Pat. No. 4,794,096.

In general, the oligomeric aluminoxane compounds obtained in this wayare in the form of mixtures of chain molecules of various lengths, bothlinear and cyclic, so that m is to be regarded as a mean value. Thealuminoxane compounds can also be present in admixture with other metalalkyls, preferably aluminum alkyls.

Other compounds which can be used as compounds capable of formingmetallocenium ions are aryloxyaluminoxanes as described in U.S. Pat. No.5,391,793, aminoaluminoxanes as described in U.S. Pat. No. 5,371,260,aminoaluminoxane hydrochlorides as described in EP-A 633 264,siloxyaluminoxanes as described in EP-A 621 279 or mixtures thereof.

The process of the present invention leads to a considerable reductionin deposit formation in the gas-phase reactor and thus to significantlylonger running times. This requires no additional installations and noadditional regulating systems. The following examples illustrate theprocess.

EXAMPLES Example 1 Production of a Supported Chromium Catalyst

185 g of silica gel (SG 332, from Grace, Germany) were suspended in 400ml of a 3.56% strength by weight solution of Cr(NO₃)₃.9H₂O in methanol.The methanol was subsequently distilled off under reduced pressure andthis catalyst precursor was activated at 650° C. in the presence ofoxygen.

Example 2 Production of an Antistatically Modified Chromium Catalyst

The oxides having an antistatic effect (mean particle size 50 μm) weredried at 250° C. under reduced pressure for 8 hours and subsequentlyflushed with nitrogen. The oxide powder was then mixed in the ratiosindicated in Table 1 with the catalyst precursor produced as inExample 1. This mixture was subsequently activated at 650° C. in thepresence of oxygen.

Examples 3 to 10 Polymerization of Ethylene in the Presence of theAntistatic Oxides

The polymerization experiments were carried out in the gas phase at 110°C. and an ethylene pressure of 40 bar in a stirred 11 autoclave. Theelectrostatic potential was measured during the polymerization using aprobe as is customary for the measurement of electrostatic charging. Thereaction times and the experimental results are shown in Table 1.

TABLE 1 Polymerization of ethylene in the presence of MgO and/or ZnOOxide Polymer Productivity Polymeriz- Electric Modified catalystscontent density Yield g of PE/g of ation time potential Ex. producedfrom [%] [g/cm³] [g] cat. [min] [V] 3 Precursor (55.30 g) and 1.0 0.9551135 2000 90 ±75 MgO (0.56 g) 4 Precursor (43.51 g) and 0.5 0.9558 2052700 60 ±80 MgO (0.22 g) 5 Activated catalyst 1.0 0.9518 160 2600 90 ±70(45.63 g) and MgO (0.46 g) 6 Activated catalyst 0.5 0.9560 200 2900 90±85 (49.73 g) and MgO (0.25 g) 7 Precursor (48.52 g) and 1.0 0.9534 2604200 80 ±60 ZnO (0.49 g) 8 Precursor (53.23 g) and 0.5 0.9526 185 370090 ±75 ZnO (0.27 g) 9 Activated catalyst 1.0 0.9545 240 4000 90 ±60(46.45 g) and ZnO (0.47 g) 10 Activated catalyst 0.5 0.9563 240 4600 90±65 (46.45 g) and ZnO (0.21 g) Comparative example 0.9549 225 2600 70−2500  without antistatic agent without antistatic Comparative example0.9506 210 2600 70 −2300  agent

We claim:
 1. A process for the gas phase polymerization of α-olefinswhich comprises: 1) polymerizing the α-olefins at temperatures of from30 to 150° C. and pressures of from 5 to 80 bar, 2) in the presence of acatalyst mixture containing a) a catalyst and b) 0.1 to 5% by weight,based on the total amount of the catalyst mixture, ZnO and/or anhydrousMgO as an antistatic agent, and where 3) said catalyst mixture does notcomprise: a) a chromium catalyst, and b) a MgO-supported Zieglercatalyst modified both with an alkene and with alkylaluminum hydride,and c) free MgO, where the total amount of MgO is not less than 2% byweight of the catalyst mixture, wherein the catalyst and the ZnO and/orMgO antistatic agent are premixed prior to contact with the olefins. 2.A process as claimed in claim 1, wherein a supported chromium catalystis used as a constituent of the catalyst mixture.
 3. A process asclaimed in claim 2, wherein the chromium catalyst is prepared by addingthe desired amount of MgO and/or ZnO to the inactive catalyst precursorand subsequently activating this mixture in a customary manner.
 4. Aprocess as claimed in claim 1, wherein a Ziegler catalyst orZiegler-Natta catalyst is used as a constituent of the catalyst mixture.5. A process for the gas phase polymerization of α-olefins whichcomprises: 1) polymerizing the α-olefins at temperatures of from 30 to150° C. and pressures of from 5 to 80 bar, 2) in the presence of acatalyst mixture containing a) a metallocene catalyst and b) from 0.1 to5% by weight, based on the total amount of the catalyst mixture, ZnOand/or anhydrous MgO as an antistatic agent, and where 3) said catalystmixture does not comprise: a) a chromium catalyst, and b) aMgO-supported Ziegler catalyst modified both with an alkene and withalkylaluminum hydride, and: c) free MgO, where the total amount of MgOis not less than 2% by weight of the catalyst mixture, wherein thecatalyst and the ZnO and/or MgO antistatic agent are premixed prior tocontact with the olefins.
 6. A process for the gas phase polymerizationof α-olefins which comprises: 1) polymerizing the α-olefins attemperatures of from 30 to 150° C. and pressures of from 5 to 80 bar, 2)in the presence of a catalyst mixture containing a) a catalyst and b)from 0.1 to 5% by weight, based on the total amount of the catalystmixture, ZnO as an antistatic agent, and where 3) said catalyst mixturedoes not comprise: a) a chromium catalyst, and b) a MgO-supportedZiegler catalyst modified both with an alkene and with alkylaluminumhydride, and c) free MgO, where the total amount of MgO is not less than2% by weight of the catalyst mixture wherein, the catalyst and the ZnOand/or MgO antistatic agent are premixed prior to contact with theolefins.
 7. A process as claimed in claim 1, wherein the antistaticagent is present in the catalyst mixture in an amount of more than 0.2%by weight and less than 2% by weight.
 8. A process as claimed in claim1, wherein ethylene is polymerized as α-olefin.
 9. A process as claimedin claim 1, wherein a mixture of